This invention relates to an illumination apparatus, a projection exposure apparatus including the illumination apparatus, and a device fabricating method using the exposure apparatus, and more particularly to an illumination apparatus suitably applicable to a projection exposure apparatus used in the lithography process upon fabrication of devices such as semiconductor devices.
Recently, a projection exposure apparatus for fabricating a very large-scale integrated circuit (VLSI) or other semiconductor devices that achieve large packaging densities requires uniform illuminance distribution and high telecentricity of beams incident upon a wafer (or substrate) during circuit patterning process.
In general, a semiconductor device is fabricated through a plurality of rounds of the lithography process. Therefore, if the telecentricity of beams incident upon a wafer decreased, an image would shift when a different circuit pattern is overlaid and exposed on the same surface of the wafer on which steps were formed during the previous round of the lithography process, which would disadvantageously make it impossible to obtain a high precision semiconductor device. The decrease of the telecentricity of beams incident upon a wafer would be derived, for example, from a geometrical optical shift due to errors during manufacture of the projection system, a shift of light quantity baricenter due to nonuniform transmittance of dielectric multilayer film in an optical device of the projection system, a geometrical optical shift due to errors during manufacture of the illumination system or errors during movement of a movable part when a change is made in value 6 represented by a ratio of the number of apertures in the projection system to the number of apertures in the illumination system or when a change is made in illumination methods between normal illumination and slanting illumination, a shift of light quantity baricenter due to nonuniform transmittance of dielectric multi-layer film in an optical device of the illumination system, or the like. It goes without saying that the above factors would not only take place singly, but also conspire to take place simultaneously.
In order to correct the telecentricity on an illuminated surface, for example, a projection exposure apparatus (projection aligner) as disclosed in Japanese Laid-Open Patent Application, Publication No. 9-26554 corresponding to U.S. Pat. No. 5,739,899 has two-stage fly-eye lenses as amplitude division type integrators disposed in series in an optical path of the illumination system, and a light emitted through the first fly-eye lens is Kohler-illuminated into a light incident surface of the second fly-eye lens, where the second fly-eye lens is comprised of two groups, the second group is moved in a plane orthogonal to an optical axis with respect to the first group, so that a direction of beams emitted through the second fly-eye lens is changed to adjust the telecentricity of the beams on an image plane.
In a technique mentioned as a prior art in the above reference, a part of the optical system posterior to the fly-eye lenses is moved in a direction orthogonal to an optical axis or in a direction parallel to the optical axis to adjust the telecentricity on the image plane in the projection system.
However, according to the adjusting methods disclosed in the above reference, the direction of beams emitted from the second fly-eye lens may change as the second group of the second fly-eye lens shifts, but in that event, the Kohler illumination of the illuminated plane using the second fly-eye lens would transversely shift an area illuminated by the illumination light. Accordingly, in order to make substantial adjustment of telecentricity feasible, a larger area than an indispensable illumination area is required illuminating by illumination light, and use efficiency of the illumination light would result. These circumstances would consequently lead to loss of throughput.
In the technique mentioned as a prior art in the above reference as well, the illumination light should disadvantageously illuminate a larger area than indispensable illumination area for fabricating semiconductor devices.
Accordingly, it is an exemplified general object of the present invention to provide an illumination apparatus that can adjust telecentricity on an image plane without reducing use efficiency of illumination light.
According to an aspect of the present invention, there is provided an illumination apparatus comprising: a first optical system for forming uniform light intensity distribution; a second optical system including an optical integrator and a condensing system for superposing a plurality of beams from the optical integrator on a surface to be illuminated; a projection system for projecting the uniform light intensity distribution onto the optical integrator of the second optical system; and a device for moving the uniform light intensity distribution in a direction across an optical axis of the projection system.
According to another aspect of the present invention, there is provided an illumination apparatus comprising: a first optical integrator of an inner surface reflection type; a first condensing system for condensing light from a light source into a light incident part of the first optical integrator; a second optical integrator of an amplitude division type; a second condensing system for superposing a plurality of beams from the second optical integrator on a surface to be illuminated; an image-forming system for forming an image of a light emission part of the inner surface reflection type optical integrator on the amplitude division type optical integrator; and a device for moving the light emission part of the inner surface reflection type optical integrator in a direction across an optical axis of the second condensing system. The device may move the light emission part in a direction orthogonal to the optical axis. The device may further move the first optical integrator in the orthogonal direction within such a range that creates no a loss of light incident onto the first optical integrator. Moreover, at least part of optical elements in the first condensing system may be moved in the direction orthogonal to the optical axis in synchronization with movement of the first optical integrator. Alternatively, the device pivots the first optical integrator about an axis orthogonal to the optical axis. The illumination apparatus may further comprise a plurality of illumination modes each of which provides a different condition for illuminating a surface to be illuminated; and a memory for storing an amount of movement of the first optical integrator for each illumination mode, wherein the first optical integrator is moved based upon information stored in the memory when the illumination mode is switched. Alternatively, the illumination apparatus may further comprise a transparent parallel flat plate that light from the first optical integrator enters, wherein light intensity distribution on the second optical integrator is changed by varying a tilt of the parallel flat plate with respect to the optical axis.
According to another aspect of the present invention, there is provided an illumination apparatus comprising: a first optical integrator of an inner surface reflection type; a first condensing system for condensing light from a light source into a light incident part of the first optical integrator; a second optical integrator of an amplitude division type; a second condensing system for superposing a plurality of beams from the second optical integrator on a surface to be illuminated; and an image-forming system for forming an image of a light emission part of the inner surface reflection type optical integrator on the amplitude division type optical integrator, wherein the light emission part of the inner surface reflection type optical integrator is moved in a direction across an optical axis of the second condensing system.
According to another aspect of the present invention, there is provided a projection exposure apparatus comprising: any one of the above-described illumination apparatuses which illuminates a reticle on which a pattern is formed; and a projection optical system for projecting the pattern on a wafer. The projection exposure apparatus may further comprise a detector for detecting telecentricity of the projection optical system, wherein the first optical integrator is moved based upon a detection result by the detector.
According to another aspect of the present invention, there is provided a device fabrication method comprising the steps of: applying a resist onto a wafer; exposing the wafer in accordance with a pattern on a reticle using a projection exposure apparatus according to any one of claims 10 and 11; and developing the wafer that is exposed with the pattern.
Other objects and further features of the present invention will become readily apparent from the following description of the embodiments with reference to accompanying drawings.